Process for the hydration of sodium tripolyphosphate

ABSTRACT

SODIUM TRIPOLYPHOSPHATE IN PARTICULATE FORM IS AT LEAST PARTIALLY HYDRATED BY CONTACT WITH STEAM DURING ITS PNEUMATIC CONVEYANCE. AN APPARATUS FOR ACCOMPLSIHING THE PROCESS COMPRISES A PIPE, AT LEAST ONE INLET THERETO FOR A CARRIER GAS AND FOR THE PARTICULATE SODIUM TRIPOLYPHOSPHATE, AT LEAST ONE INLET FOR ADMITTING STEAM TO THE PIPE AT A POINT OR POINTS PAST WHICH THE SODIUM TRIPOLYPHOSPHATE IS CONVEYED BY THE CARRIER GAS AND AN EXIT FROM THE PIPE FOR THE HYDRATED SODIUM TRIPOLYPHOSPHATE AND THE CARRIER GAS. THE APPARATUS MAY BE COUPLED TO A DETERGENT SLURRY-MAKING APPARATUS FOR DIRECT DOSING OF THE HYDRATED SODIUM TRIPOLYPHOSPHATE INTO A SLURRY-MIXER.

June 27, 1972 H. W. HORNIG ETAL PROCESS FOR THE HYDRATION 0F SODIUM TRIPOLYPHOSPHATE Filed Dec. 22, 1969 lNVE NTORS 2 HANS RNER Hb' nd KURT WALZ 44 EIR R E I United States Patent Olfice 3,672,826 Patented June 27, 1972 US. Cl. 23-106 7 Claims ABSTRACT OF THE DISCLOSURE Sodium tripolyphosphate in particulate form is at least partially hydrated by contact with steam during its pneumatic conveyance. An apparatus for accomplishing the process comprises a pipe, at least one inlet thereto for a carrier gas and for the particulate sodium tripolyphosphate, at least one inlet for admitting steam to the pipe at a point or points past which the sodium tripolyphosphate is conveyed by the carrier gas and an exit from the pipe for the hydrated sodium tripolyphosphate and the carrier gas. The apparatus may be coupled to a detergent slurry-making apparatus for direct dosing of the hydrated sodium tripolyphosphate into a slurry-mixer.

The invention relates to the production of hydrated sodium tripolyphosphate. More particularly it relates to a process and apparatus for the production of at least partially hydrated sodium tripolyphosphate, which can be suitably used for the manufacture of detergent powders.

Sodium tripolyphosphate is an important constituent as a detergency builder in detergent compositions, for ex ample washing powders made by spray-drying aqueous slurries. Its proportion of the total composition is such that its properties not only greatly influence the nature of the slurry but also have an appreciable elfect on the structure of the finished powder.

Sodium tripholyphosphate (Na P O crystallises monoclinically and occurs in two modifications, known as Phase I, which is the high temperature form, and Phase II, which is the low-temperature form. The essential difference between the two modifications is that Phase I sodium tripolyphosphate hydrates very much faster than Phase II sodium tripolyphosphate, leading to the formation of sodium tripolyphosphate hexahydrate. The rate of hydration of anhydrous sodium tripolyphosphate containing substantial proportions of Phase I material is so great that it tends to lead to the formation of hard lumps and incrustations during the slurry-making process. On the other hand, the high rate of hydration means that only a short time is required to attain substantially quantitative hydration resulting in a constant slurry viscosity.

In the production of detergent compositions, it is attempted to transform quantitatively the sodium tripolyphosphate into its hexahydrate, so as to enable the slurry, which is sprayed while hot, to produce a final powder of good flow properties and stability to storage.

In contrast to Phase I material, Phase II sodium tripolyphosphate hydrates very slowly and tends to remain as a supersaturated solution. The reluctance to hydrate is manifested in delay in reaching consistancy in the slurry viscosity. A further disadvantage is that a longer stirring time is needed, which involves the risk of increased hydrolysis of the sodium tripolyphosphate into orthoand pyrophosphate. Besides, from supersaturated Phase II sodium tripolyphosphate solutions the hexahydrate only crystallises slowly and in large crystals which have an adverse effect on the quality of some spray-dried powder compositions. Detergent powders made With sodium tripolyphosphate consisting predominantly of Phase H material, together with for example alkylbenzene sulphonate, soap and nonionic synthetic detergent active compounds, are generally soft, do not flow freely and are sticky to the touch. For this reason .it has been preferred in continuous slurry-making processes to use sodium tripolyphosphate with a high Phase I content. Nevertheless, even using sodium tripolyphosphate with a high Phase I content does not always make it possible to produce detergent powders containing relatively large proportions of anionic detergent active compounds, soap and nonionic detergent active compounds, with good free-flowing properties and in one operation, for example by a spray-drying process.

In an attempt to obviate these difficulties it has already been proposed to prepare detergent slurries with sodium tripolyphosphate which is at least partially in the form of its hexahydrate, and several suggestions have also been made on how to perform the hydration process, for example by spraying water onto sodium tripolyphosphate in a rotating drum, or by its treatment with ice or moisturised air.

The present invention now provides a simple and yet more elfective method for the production of at least partially hydrated sodium tripolyphosphate, which method comprises contacting particulate sodium tripolyphosphate with steam during its pneumatic conveyance.

The process of the invention proceeds continuously using a relatively simple apparatus and produces, at a rate that is comparatively much higher than is attainable with any other conventional method, hydrated sodium tripolyphosphate which can be used either directly for detergent slurry-making or subjected to storage and handling prior to use without any detrimental effect.

Thus the process according to the invention can be carried out as an independent process for producing partially or substantially hydrated sodium tripolyphosphate, or it can be coupled to a detergent slurry-making process in which the hydrated phosphate is directly dosed into the slurry-mixing apparatus.

In the process according to the invention particulate sodium tripolyphosphate is pneumatically conveyed through a pipe-line in which it is contacted with steam by means of one, two or more successively arranged steam jet nozzles in the pneumatic conveyor line. The number of steam jet nozzles which can be used depends upon the length of the steam-treatment conveyor pipe-line; more steam jet nozzles enables a more uniform steam-treatment or an increase in sodium tripolyphosphate throughout.

Theamount of pneumatic carrier gas can be automatically controlled by a pressure-reducing valve. Advantageously the weight ratio of sodium tripolyphosphate to carrier gas ranges from about 10:1 to 2:1, and is preferably about 5:1.

The process is suitably carried out using a steam to carrier gas weight ratio of from about 1:25 to 3:10, to produce sodium tripolyphosphate partially hydrated to the extent of up to approximately 15% moisture content, which corresponds to aproximately 65% hexahydrate content.

For detergent composition manufacturing purposes, a degree of hydration corresponding to a hexahydrate content of 4 to 9%, preferably 5 to 7% by weight, is generally adequate.

The steam jet nozzles are supplied with superheated steam of a suitable degree of saturation and perferably in such a way that the weight ratio of steam to sodium tripolyphosphate in the section at each contact point should not exceed 5:100, and the weight ratio of steam to sodium tripolyphosphate along the line lies between 0.5:100 and :100, preferably between 2:100 and 3: 100.

The degree of saturation of the steam used for the processshouldbe kept as low aspossible, i.e. so.that undesirablecondensation in thepipe feeding the nozzle is prevented and the steam is saturated when it emerges from the nozzle. This can generally be achieved by using steam having a saturation temperature of from 105C. to 150 C. and superheated to about 200 C.

As a result of the expansion in the nozzle the steam is cooled down-to such an extent that it reaches saturation and hence condenses on the sodium tripolyphosphate particles. The flow rate of the sodium tripolyphosphate at the steam contact points should preferably be adjusted to from 20 to 30 metres per second.

It has beenobserved that by the process according to the invention a large number of extremely small hexahydrate seed crystals is produced on the sodium.tripolyphosphate surface, which seed crystals will in turn initiate and materially accelerate the hydrations of sodium tripolyphosphate in a subsequent slurry preparation process, resulting in a large number of small sodium tripolyphosphate hexahydrate crystals. The hexahydrate crystals formed on the sodium tripolyphosphate surface and discernible under the microscope all have a size less than 20/4. The actual seed crystals are in the size range of approximately 1-3/4, and larger crystals which may also be observed under the microscope on the sodium tripolyphosphate surface are agglomerates of smaller seed crystals, which will be set free again during the solution of the sodium tripolyphosphate in the slurry. 1

During the hydration process the temperature of the sodium tripolyphosphate may increase to approximately 50 C.-60 C. due to the heat of hydration and heat of condensation, but this increase has no substantial adverse efiect on the sodium tripolyphosphate quality. An examination as to any possible hydrolysis of sodium tripolyphosphate treated according to the invention has shown that on comparing the average results of analysis of 30 samples of untreated and 12 samples of steam-treated sodium tripolyphosphate, there is no increase in orthophosphate content, the pyrophosphate content in the steamtreated material is only 1.2% higher than in the untreated material, and there is only a dilference of 1.1% in the tripolyphosphate content, which has no appreciable adverse elfect on the quality of the sodium tripolyphosphate as a detergency builder. 1

Detergent slurries prepared with sodium' tripolyphosphate hydrated according to the invention are found to produce on spray-drying hard, crisp and free-flowing powders. It has previously been observed that the size and shape of the hexahydrate crystals formed in the slurry are of decisive importance for the quality of'the detergent powder; the smaller the crystals, the better thepowder structure. This is particularly true for so-calledlow sudsing detergent compositions which are based onternary mixtures of anionic and nonionic detergent active compounds and soap.

With sodium tripolyphosphate hydrated according to the invention, hexahydrate crystals in the order of (1-10) x (5--20)y., preferably in the order of (l-3) x (640), can be obtained in the slurry, which on spray-drying produces hard and free-flowing powders of extremely good quality; this is thought to be due to the presence of such small hexahydrate crystals in the powder.

The process according to the invention is applicable to any sodium tripolyphosphate quality ranging from very low Phase I to very high Phase I content sodium tripolyphosphate, though the greatest benefit is experienced from very low Phase I sodium tripolyphosphate-(high Phase II sodium tripolyphosphate) rather than from the. high Phase I product.

Surprisingly, therefore, the method according to the invention makes it possibly when producing a washing powder with good flow properties to refrain from using the more expensive high Phase 1 sodium tripolyphosphate and to use the cheaper commercially available material consisting mainly of the Phase II material, for example sodiumtripolyphosphate comprising at least 90% by weight of Phase II material, evenin those cases where the use of anhydrous high Phase I content sodium.tripolyphosphate (e.g. -45% Phase I) would still produce unsatis-l factory crawly powders, namely low-sudsing composi; tions comprising high proportions of ternary mixtures of detergent active compounds.

In one embodiment of theinvention-hydration. of the sodiumtripolyphosphate is. carried out during the pneumatic conveyance of the sodium tripolyphosphate from the silo to the detergent slurry making plant. p l

Accordingly the invention also comprisesa process for the preparation of detergent compositions comprising. the

step of at least partially hydrating sodium, tripolyphosphate during its pneumatic conveyanceas described above.

The process of the invention can be used for the preparation of all sorts of detergent powder compositions comprising sodium tripolyphosphate, suchas those current commercial detergent compositionsbased on anionic;detergent active agents, soap or nonionic detergent. active agents, or mixtures thereof, and also other compositions having a, fairly high content of rdetergent: activecompounds, but it isof particular advantage for the manufacture of detergent powder compositions which contain ternary mixtures of anionicandnonionic detergent active compounds and soap. I

The term anionic detergent active compounds is used in this specification to designate synthetic anionic detergent activecompoundswhich are broadly described as the water soluble salts, particularly the alkali metal salts, of organic sulphuric or phosphoric reaction products having in the molecular structure a hydrocarbon radical containingfrom 8 to about 22 carbon atoms and a radical selected from the group consisting of sulphonic acid, sulphuric acid ester or phosphoric acid ester radicals. Important examples of the syntheticanionic detergent active compounds normallyused in detergent compositions are the sodium and potassium alkylbenzenesulphonates;sodium and potassium alkyl sulphatestwater soluble alkane; alkene and olefin sulphonates; alkali metal alkyl phosphates; alkali metal salts ofzsulphated or phosphated alkylene oxide condensation products prepared by ethoxylation and/ or propoxylation of various orgaic hydrophobic compounds containing active hydrogen, such as alcohols, mercaptans and alkyl phenols; sodium -alkyl glyceryl-..ether sulphates; and the like. The term olefin sulphonate. is used abovev to describe thematerial obtained by the hydrolysis and neutralisation of the reaction product of sulphonation of an olefin.,,The material is a mixture, of predominantly alkene sulphonates and hydroxyalkane sulphonates with lesser amounts, of the disulphonates.=

The term nonionic detergent active compounds" is used to referbroadly tosynthetic compounds produced by the condensationof an'alkylene oxide withan organic hydrophobic compound, which may be aliphaticor-alkyl aromatic in nature. The length of the hydrophilic, or polyoxyalkylene, radical which is, condensed with any particular hydrophobic group can bev readily, adiusted, to yield a water-soluble compound having the desired degree of balance between the .hydrophilic and hydrophobic elements. Examples of suitable nonionicdetergent active compounds ar'ecthylene oxide'condensation products of pnmary'or secondary, branched or unbranched higher alcohols; alkyl-phenol ethylene oxide and/or propylene oxide condensation products; compounds obtained from the condensation of ethylene oxide with a hydrophobic base' forr'ried by-the condensation ofp'ropylene oxide with propylene glycol; fatty acid amides condensed 'with ethylene 'oxide, and the like. p

a The term soap is used hereto denote water soluble salts, usually sodium and/or potassium salts, of ;long chain fatty acids of naturally occurring 'vegeta'ble'or animal esters, or of fatty acids produced synthetically (e.g. by the oxidation of petroleum or the hydrogenation of carbon monoxide by the Fischer-Tropsch process), of resin acid (e.g. rosin and the resin acids in tall oil), and/or naphthenic acids.

As stated above, the process according to the invention can be accomplished using a relatively simple apparatus.

Accordingly, in a further aspect, the invention comprises an apparatus for the production of at least partially hydrated sodium tripolyphosphate, comprising a pneumatic conveyor pipe with at least one inlet thereto for a carrier gas and for particulate sodium tripolyphosphate, at least one inlet for admitting steam to the pipe at a point or points past which the sodium tripolyphosphate is conveyed by the carrier gas and an exit from the pipe for steam-treated sodium tripolyphosphate and the carrier gas.

The steam inlet means are constituted by steam jet nozzles, and should preferably be fitted coaxially and concurrently with the flow in the pipe, in such a way that the sodium tripolyphosphate flows uniformly around them. This arrangement helps to minimise wetting the wall of the pipe and consequent incrustation on the wall.

An apparatus according to the invention is illustrated by way of example in the accompanying drawing, the single figure of which is a diagrammatic plan view, partly in section, in which the direction of flow through the apparatus is indicated by arrows. In the drawing a storage container for particulate sodium tripolyphosphate is situated above the conveyor pipe 1 and shown in outline by a chain-dotted line 2. Sodium tripolyphosphate is discharged from the container by a bucket wheel -valve 3, which is driven by an electric motor 4, to the pneumatic conveyor pipe 1. Air from an air-main 5 is admitted to the pipe 1 through a reducing valve 6 to pneumatically convey the particulate sodium tripolyphosphate through the pipe 1 to an intermediate storage container 7, from which the treated sodium tripolyphosphate is withdrawn for slurry-making (by means not shown).

A steam line 8 containing an orifice plate 9 connects with four steam inlet nozzles 10a, 10b, 10c and 10d, situated successively and at regular intervals in the pneumatic conveyor pipe 1. Four water-traps 11a, 11b, 11c and 11d are located between the steam line 8 and the nozzles 10a to 10d, respectively. The pipe 1 in the region of the steam nozzle 10a is shown in section to show the coaxial tip 12 of the nozzle.

The steam treatment conveyor pipe terminates at a separator 13 which is mounted directly on top of the intermediate storage container 7. An outlet pipe 14 leads to dedusting filters (not shown) where the air is further treated.

The invention is further illustrated by the following examples in which an apparatus of the type shown in the accompanying drawing was used. All percentages given are by weight.

EXAMPLE 1 Commercial quality sodium tripolyphosphate, containing 8% Phase I material, was discharged from a storage container by a bucket wheel valve into a 19 metres long steam-treatment conveyor pipe-line, along which the sodium tripolyphosphate was conveyed by compressed air at a pressure of about 1.5 atmospheres to an intermediate storage tank.

The amount of sodium tripolyphosphateconveyed was 3500 kg. per hour. The quantity of air for conveying the sodium tripolyphosphate was automatically regulated by a pressure-reducing valve at approximately 500-550 cubic metres per hour, measured at 'N.T.P.

The steam-treatment conveyor pipe had an internal diameter of 10 cm. and led to an intermediate storage tank with a discharge for dosing into a detergent slurrymaking plant. 7

Four steam jet nozzles, which were supplied with steam at a pressure of 9 atmospheres each had a capacity of 20-60" kg. steam per hour. They were fitted coaxially in the pipe and were each supplied with 20 kg. per hour of 5 steam, which was dried prior to reaching the nozzles.

The partially hydrated sodium tripolyphosphate col lected in the intermediate storage tank had a degree of hydration corresponding to a hexahydrate content of approximately 7%, had a size distribution not substantially difierent from that of the anhydrous powder, and was dry and free-flowing and suitable for use directly as a raw material in the manufacture of built detergent compositions.

EXAMPLE tr A detergent powder of the following composition was made using the partially hydrated sodium tripolyphosphate as produced in Example I by forming a slurry and subsequently spray-drying it in a spray-tower in the known way.

Composition: Percent Alkyl benzene sulphonate 5.1

Nonionic detergent active compound (nonylphenol-14 EO) 9.9

Soap 3.8

Sodium carboxymethylcellulose 1.3 Sodium tripolyphosphate (calc. on anhydrous basis) v 42.3

Alkaline silicates 10.0

Salts, mainly sodium sulphate 15.2

Water, optical brightener 12.4

EXAMPLES III AND IV The process of Example I was repeated with the exception that in Example III a sodium tripolyphosphate containing 20% Phase I material, and in Example IV, a sodium tripolyphosphate containing Phase I material were used. 7

Both hydrated sodium tripolyphosphates obtained showed the same good properties as that of the product of Example I, all products being extremely manageable and behaving very well on storage.

What is claimed is:

1. A process for the production of particulate hydrated sodium tripolyphosphate comprising:

(i) introducing particulate sodium tripolyphosphate and a carrier gas into a conveyor pipe-line, (ii) pneumatically conveying said particulate sodium tripolyphosphate through said conveyor pipe-line by said carrier gas, (iii) admitting superheated steam into said pipe-line thereby contacting said tripolyphosphate with said steam while being conveyed by said carrier gas,

(iv) adjusting the weight ratio of said steam to said carrier gas to between about 1:25 to 3:10, and the weight ratio of said sodium tripolyphosphate to said carrier gas to between about 10:1 and about 2:1,

thereby converting at least a portion of the tripoly- 9% by' 'weight ofsaid particulate hydrated sodium tripolyphosphate. 1 3. A process according to claim l'wherein the sodium tripolyphosphate is contacted with the steam at two-or more points during its pneumatic conveyance; 7 r v 4. A process according to claim 1 wherein the, ratio by weight of steam to sodium tripolyphosphateis from 0.5:100to 5:100. 3

v 5. A process accordingto claim 1 wherein the steam is superheated to about200 C. and has a saturation temperature of from 105 C. to 150 C.

6.' A process according to claim 1 wherein the flow rate of the sodium tripolyphosphate at the steam contact points is from 20 to 30 metres per second.

7. A process according to claim 1 wherein the sodium tripolyphosphate comprises at least 90 percent by weight of Phase II material.

,8 .References Cited- UNITED, STATES PATENTS 3,423,321 l/1969 Shaver 23-106 5 3,390,093 6/1968 Fe'ierstein et' al.' 23-107 X 3,336,104 8/1967 .tMiller ;i' 23-106"x 3,063,801 11/1962 Groves l f 2 4 1 FOREIGN PATENTS 742, 23 f 12/1955 'Grea t'Biritain 23106 A 09,783 10/1948 (316 1311161 1 23- 10,6'A

OSCAR'R. YERTIMZV, Primary Examiner C. B. RODMAN, Assistant Examiner 15 Y 

